Method for coating coils

Abstract

A method of coil coating a metal strip that includes applying to the metal strip, a coating composition that includes a binder containing a) a polyol component, which is soluble or dispersible in water; and b) a polyisocyanate component, which is soluble or dispersible in water and has blocked isocyanate groups. Metal substrates coated according to the method can be used to make articles.

1 . A method of coil coating for coating a metal strip comprising applying to the metal strip a coating composition comprising a coating containing 
 a) a polyol component, which is soluble or dispersible in water; and    b) a blocked polyisocyanate component, which is soluble or dispersible in water.    
   
   
       2 . The method according to  claim 1 , wherein the polyol in a) comprises the reaction product of a polyisocyanate component containing 50 to 100 wt. % of a polyisocyanate selected from the group consisting of 4,4′-diisocyanatocyclohexylmethane (HMDI), hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethyl-cyclohexane (IPDI), 2,4- and/or 2,6-diisocyanatotoluene (TDI), 1-methyl-2,4-diisocyanatocyclo-hexane, 1-methyl-2,6-diisocyanatocyclohexane and 4,4′-diisocyanatodiphenyl-methane (MDI), and combinations thereof; 
 a polyol component containing one or more polyether polyols and having an OH number of 25 to 350 mg KOH/g solids; and    an isocyanate-reactive component containing at least one group capable of salt formation.    
   
   
       3 . The method according to  claim 2 , wherein the polyisocyanate comprises 4,4′-diisocyanatodicyclohexylmethane,  
   
   
       4 . The method according to  claim 1 , wherein the blocked polyisocyanate in b) comprises the reaction product of a polyisocyanate having an isocyanurate group content of 5 to 30 wt. %, a reversible, monofunctional blocking agent for isocyanate groups, a nonionic hydrophilic component and a stabilizing component which has 1 to 2 hydrazide groups and a molecular weight of 70 to 300.  
   
   
       5 . The method according to  claim 1 , wherein the equivalent ratio of blocked isocyanate groups of component b) to hydroxyl groups of component a) is from 0.8:1 to 3:1.  
   
   
       6 . The method according to  claim 1 , wherein the coating composition further comprises a catalyst.  
   
   
       7 . The method according to  claim 6 , wherein the catalyst includes one or more catalysts selected from the group consisting of tertiary amines, tin(II) octoate, dibutyltin oxide, and dibutyltin dilaurate.  
   
   
       8 . The method according to  claim 1 , wherein the coating composition further comprises a flow control additive.  
   
   
       9 . The method according to  claim 8 , wherein the flow control additive includes one or more flow control additives selected from the group consisting of polyacrylic esters, non-ionic fluorinated alkyl ester surfactants, non-ionic alkylarylpolyether alcohols, and silicones.  
   
   
       10 . The method according to  claim 1 , wherein the binder comprises a polyol component, which is the reaction product of 
 A1) 20 to 60 wt. % of a polyisocyanate component containing 50 to 100 wt. % of 4,4′-diisocyanatodicyclohexylmethane and 0 to 50 wt. % of other organic polyisocyanates having a molecular weight of 140 to 1500,    B1) 20 to 60 wt. % of a polyol component containing one or more polyether polyols and having an OH number of 25 to 350 mg KOH/g solids,    C1) 2 to 12 wt. % of an anionic or potential anionic component containing one or more compounds having at least one isocyanate-reactive group and at least one group capable of salt formation, which may optionally be present in at least partially neutralized form,    D1) 0 to 12 wt. % of a nonionic hydrophilic component containing one or more compounds which are mono- or difunctional for purposes of the isocyanate addition reaction and have at least one lateral or terminal hydrophilic polyether chain,    E1) 0 to 15 wt. % of one or more polyhydric alcohols having 2 to 4 hydroxyl groups and a molecular weight of 62 to 250,    F1) 0 to 15 wt. % of one or more (cyclo)aliphatic polyamines having 2 to 4 amino groups and a molecular weight of 60 to 300,    G1) 0 to 30 wt. % of one or more (cyclo)aliphatic polyamino/hydroxyl compounds having a total of 2 to 4 hydroxyl and amino groups and a molecular weight of 61 to 300 and    H1) 0 to 15 wt. % of one or more stabilizing components which are mono- or difunctional for purposes of the isocyanate addition reaction and have 1 to 2 hydrazide groups and a molecular weight of 70 to 300,    wherein the percentages of A1) to H1) add up to 100.    
   
   
       11 . The method according to  claim 1 , wherein the binder comprises a blocked polyisocyanate component, which is the reaction product of 
 A2) 40 to 80 wt. % of a polyisocyanate having an isocyanurate group content (calculated as C 3 N 3 O 3 ; molecular weight=126) of 2 to 30 wt. % and prepared from one or more diisocyanates having a molecular weight of 140 to 350 with    B2) 5 to 30 wt. % of one or more reversible blocking agents for isocyanate groups which are monofunctional for purposes of the isocyanate addition reaction,    C2) 0 to 15 wt. % of an anionic or potential anionic component containing one or more compounds having at least one isocyanate-reactive group and at least one group capable of salt formation, which may optionally be present in at least partially neutralized form,    D2) 5 to 30 wt. % of a nonionic hydrophilic component containing one or more compounds which are mono- or difunctional for purposes of the isocyanate addition reaction and have at least one lateral or terminal hydrophilic polyether chain,    E2) 0 to 15 wt. % of one or more polyhydric alcohols having 2 to 4 hydroxyl groups and a molecular weight of 62 to 250,    F2) 0 to 15 wt. % of one or more (cyclo)aliphatic polyamines having 2 to 4 amino groups and a molecular weight of 60 to 300 and    G2) 0.5 to 15 wt. % of one or more stabilizing components which are mono- or difunctional for purposes of the isocyanate addition reaction and have 1 to 2 hydrazide groups and a molecular weight of 70 to 300.    
   
   
       12 . The method according to  claim 1  further comprising applying, before the coating composition is applied to the metal strip, a primer layer comprising a primer composition selected from the group consisting of epoxy primers, urethane based primers, polyester based primers, and water-reducible acrylic primers.  
   
   
       13 . The method according to  claim 1 , wherein the coating composition forms a coating layer having a dry film thickness of from 1 to 35 μm.  
   
   
       14 . The method according to  claim 12 , wherein the dry film thickness of the primer layer is from 1 to 35 μm.  
   
   
       15 . The method according to  claim 1 , wherein the peel strength of a dry film of the coating composition is from 2102 newton/meter (N/m) (12 lb/in) to 6130 N/m (35 lb/in) when measured in accordance with the ASTM D429 Method B 90° stripping test.  
   
   
       16 . The method according to  claim 1 , wherein the metal comprises aluminum, zinc, iron, steel, and/or nickel.  
   
   
       17 . The method according to  claim 1 , wherein the coating composition is cured at a temperature of from 1500 to 400° C. for from 20 to 150 seconds.  
   
   
       18 . A metal substrate coated according to the method of  claim 1 .  
   
   
       19 . The metal substrate according to  claim 18 , wherein the metal comprises aluminum, zinc, iron, steel, and/or nickel.  
   
   
       20 . An article comprising the metal substrate of  claim 18 .  
   
   
       21 . An article comprising a first metal substrate according to  claim 18 , and a second metal substrate according to  claim 18 , positioned such that the coated surfaces of each substrate are parallel to and opposite each other, and a reaction injection molding (RIM) composition is placed there between by the RIM process.  
   
   
       22 . The article according to  claim 21 , wherein the RIM composition comprises a foam obtained by a RIM process comprising: 
 c) mixing (1) an isocyantate-reactive component comprising: 
 i) from 5 to 80% by weight, based on the total weight of the isocyanate-reactive component, of one or more isocyanate-reactive materials having a functionality of isocyanate reactive groups of at least 1 and a number average molecular weight of from 400 to 10,000;  
 ii) a chain extender or crosslinking agent;  
 iii) a blowing agent;  
 iv) a catalyst; and  
 v) optionally; flame retardants, pigments, dyes, fillers, surfactants, flow aides, and combinations thereof; with  
 (2) an organic polyisocyanate in an amount such that the equivalent ratio of isocyanate groups to isocyanate reactive groups is from 0.8:1 to 1.3:1 and  
   d) introducing the mixture from a) into a space between the first metal substrate the second metal substrate.    
   
   
       23 . The article according to  claim 22 , wherein the blowing agent includes one or more blowing agents selected from the group consisting of water, halogenated hydrocarbons, low boiling hydrocarbons, p-toluene sulfonyl hydrazide, sodium bicarbonate, 2,2′-azobisisobutyronitrile, azodicarbonamide, 4,4′-oxy-bis(benzenesulfonyl hydrazide), dinitrosopentamethylene-tetramine, air, nitrogen, carbon dioxide, and argon.